ORIGIN OF SPECIES. 1 1 



one condition of life, there could bo no change of species. Of course such an absolute unifor- 

 mitj'- of heat could not exist ; a pot, although boiling, has not in every point the same 

 degree of heat, therefore different degrees of temperature, in other words, different physical con- 

 ditions which might give rise to new species, must at all times have existed on our planet ; but, 

 as in the parallel of the boiling pot, they would not be great (so might often be ineffective), 

 and would not be permanently fixed for any time upon one spot, so that although new species 

 might occasionally bo developed, special provinces, or fauna, cuuld not exist, or at least could 

 only do so when the internal heat had been so far reduced as to allow external influences to bestow 

 a more or less iiermanent character upon particular spots. The greatest change of all, however, 

 must have occurred at the glacial epoch, when probably for the first time in the history of the 

 globe organic life made acquaintance with frost and snow. Then, if there is any truth in my thcorj% 

 a universal change must have taken place ia everything that was exposed to that cold ; that is, 

 in fact, in everything beyond the tropics. 



Now, in relation to this latter point, we find that in none of the strata of a date anterior 

 to the glacial cold are the remains of any boreal animal to be found. Every creature adopted 

 for life in a cold country appears to have been developed, subsequent to that epoch. For examjjle, 

 the mice and the voles are two nearly allied creatiu-es, the former of which is adapted to mild 

 countries, the latter to cold. No mice or rats are found in the arctic circle, but voles abound ; 

 no voles occur in the tropics or warmer temperate regions, but mice are abundant. So the fossil 

 remains of mice are found in the tertiary as well as the recent deposits, but none of any vole 

 until the dilixvium deposited subsequent to the conamencement of the glacial epoch. The same 

 is to be observed of aU boreal animals that I know of, and I bebeve the rule is universal. I 

 apprehend that the change which took place in the northern hemisi^here at the glacial epoch 

 was absolute : nothing that remained to abide the influence of the cold could escape alteration. 

 Whatever escaped change did so by taking to flight to the south, and carrjang its climate and 

 conditions of life with it. I shall have to discuss these points more at large and in- detail hereafter. 

 It is suflficient here to indicate the support that they seem to give to my hypothesis of the origin 

 of species. 



The facts relating to the appearance of species in the earlier geological formations seem 

 to accord not less exactly with the requirements of this hj-pothesis. Geologists inform us that 

 in the earlier periods of the world's history the changes of life in the sea (and there appears 

 no reason to suppose that a different law should regulate life in the sea from life on the land) 

 were accomplished at a rate much less rapid than that which prevailed in later times. The 

 premises from which they derive these inferences are no doubt imperfect. Thej' do so by com- 

 paring the depth of sedimentary rocks in which indications of life have been found, in the palaeozoic, 

 the mesozoic, and the cajnozoic periods. f They assume the amoimt of changes of life on the wliolc 

 to be equal in eacli of these jieriods, — an assumption which is, perhaps, not warranted, — and 

 having done so, find, according to Prof. Phillips, the rate of jjrogressive change to be y^ for 

 palaeozoic, jL for mesozoic, and + for ctcnozoic timc.X 



If the projjortion thus given by Professor Phillips for caenozoic and palaeozoic time be 

 anything like correct, or \ to y'g, we have, I submit, a strong confirmation of the truth of the 



♦ Sec Geological Diagram. 



X Profe.'ssor Phillips, iu "Quarterly Journ Geul. Soc.," vol. xvi. part 2, p. 1. (May, 18G(.i.) 



